1. Technical Field
The invention generally relates to the field of mechanical locking systems for floorboards, and to floorboards provided with such locking systems; blanks for such locking systems; and methods for making floorboards with such locking systems. The invention is particularly suited for use in mechanical locking systems of the type described and shown, for example, in WO9426999, WO9966151, WO9966152, SE 0100100-7 and SE0100101-5 (owned by Valinge Aluminium AB) but is also usable in optional mechanical locking systems which can be used to join floors. The invention also relates to floors of the type having a core and a decorative surface layer on the upper side of the core.
The present invention is particularly suitable for use in floating floors, which are formed of floorboards which are joined mechanically with a locking system integrated with the floorboard, i.e., mounted at the factory, are made up of one or more upper layers of veneer, decorative laminate or decorative plastic material, an intermediate core of wood-fiber-based material or plastic material and preferably a lower balancing layer on the rear side of the core, and are manufactured by sawing large floor elements into floor panels. The following description of prior-art techniques, problems of known systems and objects and features of the invention will therefore, as a non-restrictive example, be aimed above all at this field of application and in particular laminate flooring formed as rectangular floorboards intended to be mechanically joined on both long sides and short sides. However, it should be emphasized that the invention can be used in other types of floorboards with other types of locking systems, where the floorboards can be joined using a mechanical locking system in the horizontal and vertical directions. The invention can thus also be applicable to, for instance, homogeneous wooden floors, parquet floors with a core of wood or wood-fiber-based material and the like which are made as separate floor panels, floors with a printed and preferably also varnished surface and the like. The invention can also be used for joining, for instance, of wall panels.
2. Description of Related Art
Laminate flooring usually consists of a core of a 6-11 mm fiberboard, a 0.2-0.8 mm thick upper decorative surface layer of laminate and a 0.1-0.6 mm thick lower balancing layer of laminate, plastic, paper or like material. The surface layer provides appearance and durability to the floorboards. The core provides stability, and the balancing layer keeps the board plane when the relative humidity (RH) varies during the year. The floorboards are laid floating, i.e., without gluing, on an existing subfloor. Traditional hard floorboards in floating flooring of this type are usually joined by means of glued tongue-and-groove joints (i.e., joints involving a tongue on one floorboard and a tongue groove on an adjoining floorboard) on long side and short side. When laying the floor, the boards are brought together horizontally, whereby a projecting tongue along the joint edge of one board is introduced into a tongue groove along the joint edge of an adjoining board. The same method is used on the long side as well as on the short side.
In addition to such traditional floors, which are joined by means of glued tongue-and-groove joints, floorboards have recently been developed which do not require the use of glue and instead are joined mechanically by means of mechanical locking systems. These systems comprise locking means which lock the boards horizontally and vertically. The mechanical locking systems are usually formed by machining the core of the board. Alternatively, parts of the locking system can be formed of a separate material, for instance aluminum, which is integrated with the floorboard, i.e., joined with the floorboard in connection with the manufacture thereof.
The main advantages of floating floors with mechanical locking systems are that they can easily and quickly be laid by various combinations of inward angling, snapping in and insertion. They can also easily be taken up again and used once more at a different location. A further advantage of the mechanical locking systems is that the edge portions of the floorboards can be made of materials which need not have good gluing properties. The most common core material is a fiberboard with high density and good stability usually called HDF—High Density Fiberboard. Sometimes also MDF—Medium Density Fiberboard—is used as the core.
Laminate flooring and also many other floorings with a surface layer of plastic, wood, veneer, cork and the like are made by the surface layer and the balancing layer being applied to a core material. This application may take place by gluing a previously manufactured decorative layer, for instance when the fiberboard is provided with a decorative high pressure laminate which is made in a separate operation where a plurality of impregnated sheets of paper are compressed under high pressure and at a high temperature. The currently most common method when making laminate flooring, however, is direct laminating which is based on a more modern principle where both manufacture of the decorative laminate layer and the fastening to the fiberboard take place in one and the same manufacturing step. Impregnated sheets of paper are applied directly to the board and pressed together under pressure and heat without any gluing.
In addition to these two methods, a number of other methods are used to provide the core with a surface layer. A decorative pattern can be printed on the surface of the core, which is then, for example, coated with a wear layer. The core can also be provided with a surface layer of wood, veneer, decorative paper or plastic sheeting, and these materials can then be coated with a wear layer. The core can also be provided with a soft wear layer, for instance needle felt. Such a floor has good sound properties.
As a rule, the above methods result in a floor element in the form of a large board which is then sawn into, for instance, some ten floor panels, which are then machined to floorboards. The above methods can in some cases result in completed floor panels and sawing is then not necessary before the machining to completed floorboards is carried out. Manufacture of individual floor panels usually takes place when the panels have a surface layer of wood or veneer.
In all cases, the above floor panels are individually machined along their edges to floorboards. The machining of the edges is carried out in advanced milling machines where the floor panel is exactly positioned between one or more chains and bands mounted, so that the floor panel can be moved at high speed and with great accuracy past a number of milling motors, which are provided with diamond cutting tools or metal cutting tools, which machine the edge of the floor panel. By using several milling motors operating at different angles, advanced joint geometries can be formed at speeds exceeding 100 m/min and with an accuracy of ±0.02 mm.